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The Manufacture and Agronomic Efficiency of a Partially Acidulated Phosphate Rock Fertilizer¹

ABSTRACT

North Africa phosphate rock, Gafsa type (PR), and different PR/H₃PO₄ ratios were investigated to find an efficient, partially acidulated PR fertilizer (PAPR). A monocalcium phosphate (MCP)/PR ratio of approximately 60/40, produced by 26 to 30% acidulation of PR by H₃PO₄, was the most efficient PAPR product; it requires 68 to 70% less H₃PO₄ than the amount required for manufacture of triple superphosphate (TSP).

PAPR products made in pilot plants by the "Door-Oliver" process were more efficient than those produced by the "Batch" process. Field experiments with PAPR fertilizer were carried out from 1970 to 1978. Agronomic results showed that the above product was generally equal or slightly superior to TSP in terms of P availability as detected by routine soil test methods. Models on control of the P status in several soils were established on the basis of greenhouse experiments with increasing P rates for ryegrass (Lolium perenne L).

Commercial factory production of PAPR by the "Door Oliver" process costs 30 to 35% less than that of TSP because of lower total energy and less H₃PO₄ used. An additional advantage appears to be a 50 to 65% increase in fertilizer output in factory-scale installation. In practice, higher available soil P was maintained, and at least equal crop yields were obtained with a higher rate, less frequently applied, than with the same total P rate applied more often in fractional applications. This was especially true for PAPR.

¹ Contribution from the Dep. of Soil Fertility and Plant Nutrition, N. Poushkarov Inst. of Soil Sci., Sofia, Bulgaria.

² Present address: United Nations Environment Programme, P.O. Box 47074, Nairobi, Kenya.

Received for publication April 15, 1980. Accepted for publication May 5, 1981.